This application claims priority from Swiss Application No. 1534/01, filed on Aug. 20, 2001.
The invention relates to a system for compensating for unbalance of a rotating machine part, in particular of a tool holder in a machine tool.
The use of increasingly powerful cutting materials and machines makes it possible for materials such as metal, plastics, wood, etc. to be machined at increasingly high cutting speeds. As a result, speeds above 10,000 rpm are quite customary nowadays. At these high speeds, the tools used have to be very well balanced.
Examples of possible consequences of an excessive residual unbalance are bearing damage to the spindle mounting, a poor cutting performance, insufficient surface quality and a vast reduction in the service life of the cutting edges of the tools.
If a plurality of tool components are assembled to form a tool, the entire set-up has to be balanced.
According to the current prior art, tool holders are balanced by the magnitude and the angle of the residual unbalance being determined on a balancing machine and these then being compensated for by material being removed by means of drilling, milling or grinding and/or by fitting compensating weights, e.g. screwing threaded pins into bores provided for this purpose.
These balancing methods involve high outlay and, nevertheless, frequently have unsatisfactory results.
Also known, as an alternative to these balancing methods, are systems in which, for compensating for unbalance, two rings with eccentric mass distribution are positioned with an angular offset. The rings are fastened with radially guided locking screws or by way of specific annular retaining means with axially guided locking screws. These systems have the disadvantage that, as a result of vibrations, the screws can come loose and fly off like bullets. This means that the rings on the tool holder are free and may likewise be slung away.
The object of the invention is thus to improve the balancing of rotating machine parts.
This is achieved according to one arrangement of the present invention by a system for compensating for unbalance of a rotating machine part, in particular of a tool holder in the machine tool which has a generally cylindrical outer surface. The system comprises two balancing rings which can be rotated and secured in desired angular positions in relation to one another and are provided with an unbalance. The balancing rings each have an inner surface with an annular groove formed therein and the outer surface of the rotating machine part has encircling annular grooves formed therein substantially opposite the annular grooves in the balancing rings. An elastic ring is contained in each of the annular grooves and encircling annular grooves. A locking element is provided for securing the balancing rings to the machine part.